Many vehicles, such as airplanes, ships, or spacecraft, make use of a large number of actuators, sensors, and other components. These components can sometimes be individually controlled to perform various functions. By way of example, modern day commercial and military aircraft typically include a number of components that are monitored and/or controlled by a module called an LRU. An LRU may incorporate one or more processors for controlling and/or monitoring one or more components or subassemblies of a vehicle (e.g., an aircraft). For instance, on an aircraft, an LRU may monitor and/or control one or more external devices such as an actuator, valve, motor, etc., associated with component or assembly of the aircraft. An LRU may also generate output signals which can be monitored to determine if the LRU and/or the component with which the LRU is associated is functioning properly. A few examples of some of the LRU's associated with a C-17 aircraft include an aerial delivery system controller, a sensor signal interface, an electronic engine control, a cabin pressure controller, a flight data recorder, a head-up display unit, a satellite data unit, and a flight control computer.
The term LRU reflects the notion that an LRU is able to be replaced quickly on a flight line, rather than while an aircraft is at a maintenance facility. This quality may help improve maintenance operations, since when an LRU fails, the failed LRU can be quickly replaced with a spare LRU, thereby restoring an aircraft to service while the failed LRU is sent for repair. In some instances, an LRU may also be compatible across multiple aircraft platforms, eliminating the need to maintain an inventory of multiple aircraft-specific LRUs.
Many airplane systems feature loadable LRUs whose functionality may be changed or updated by loading new software onto the LRU. This feature enables operators to modify system functionality by modifying software instead of modifying or upgrading hardware and can help reduce the total number of LRU spares maintained in inventory. In some instances, loading new software may provide the ability to meet new requirements, incorporate design improvements, and/or correct errors without physically modifying or replacing hardware components. Furthermore, an operator may be able to load new software during the time required to turn an airplane around for the next flight.
In practice, software can be transferred to an LRU using various types of equipment. By way of example, software can be loaded using a permanently installed onboard loader, a portable onboard loader, industry-available shop loaders, supplier-unique shop loaders, or supplier automated test equipment. These devices use a wired, physical connection with the LRU to load the software. Further, the equipment for loading software may vary across different types of LRUs.